1. Field of the Invention
This invention relates to a method of manufacturing an extra fine wire capable of being used as an electronic lead wire, a bonding wire or a wire for extremely small magnets and, more particularly, to a method of obtaining an intermediate blank wire superior in drawing workability within an extra-fine-wire range, in which there is a reduced possibility of wire breakage even if the intermediate blank wire is drawn at ordinary temperatures. "Extra fine wire" is generally a wire equal to or less than 0.06 mm in diameter.
2. Prior Art
Methods of manufacturing an extra fine wire are known, which include (A) a method in which a drawing machine comprising multistage pulleys and a die assembly is employed to draw wire material continuously while spraying an appropriate amount of air-cooled lubricating oil, and (B) a method in which wire material is drawn while being immersed, together with a drawing die assembly, in low-temperature liquefied gas, as disclosed in Japanese Patent Publication (Kokoku) No. 54-17706.
The above-mentioned wire-drawing method (A) has the following problems. Because of frictional heat produced between the dies and the blank wire during the wire-drawing, the material strength of the blank wire is lowered due to dynamic recovery and recrystallization of the blank wire. In connection with this, the blank wire does not recover the ductility. When the blank wire, having repeatedly been drawn, is further drawn to an extra fine wire, equal to or less than 0.06 mm in diameter, breakage of the wire during drawing occurs frequently.
As described above, it is inevitable that using the above method (A) for drawing the blank wire into an extra fine wire at ordinary temperatures causes breakage of the wire to occur frequently. Because of this, the above-mentioned method (B) was developed for the purpose of obtaining an extra fine wire by processing within a low-temperature range which improves workability. However, method (B) requires a large refrigerant tank for accommodating therein the die assembly and the multistage pulleys, and also requires a great deal of cooling energy for cooling the entire system. Furthermore, it is impossible for method (B) to completely eliminate wire-breakage troubles during the production of extra fine wire. If wire breakage occurs, it takes a considerable time for inspection and repair. Thus, the method (B) cannot be said to be practical.